Neisseria gonorrhoeae has a serious impact on women=s health due to the frequency with which this pathogen infects the upper reproductive tract, and the resultant serious complications (e.g., chronic pelvic pain, involuntary infertility and ectopic pregnancy). Current models for studying gonococcal pathogenesis are limited in their ability to sufficiently mimic the intricate balance of host factors in the female reproductive tract. Therefore, the long-term objectives of this proposal are to further develop a female mouse model of gonorrhea for studying the adaptation of N. gonorrhoeae to the host in terms of phase and antigenic variation of surface molecules and gene expression in vivo. The specific aims designed to achieve this objective are to: i. further characterize experimental infection of estradiol-treated mice for use as a research tool for studying specific aspects of gonococcal genital tract infection; ii. identify the host factor(s) that play a role in the selection for gonococcal opacity (Opa) protein expression during experimental infection and to test the capacity of an Opa-specific immune response to drive antigenic variation of Opa phenotype in vivo; iii. identify gonococcal genes that are induced during experimental murine infection using reporter gene fusions. The proposed experiments designed to address these aims are: i.) the susceptibility of estradiol- treated outbred (SLC:ddY) and inbred (BALB/6) mice to N. gonorrhoeae will be characterized with regard to duration of infection and degree of inflammation. Upper reproductive tract infection will be assessed in terms of bacterial interactions with the murine endometrium; ii.) host factors that select for Opa-positive gonococci in vivo will be studied by monitoring Opa protein expression in neutrophil-depleted mice, complement-deficient mice and inbred mice that uniformly do not produce inflammation in response to infection. The PI will compare the Opa phenotype of vaginal isolates from unimmunized mice and from mice immunized with a single purified Opa protein antigenic variant to determine if an Opa-specific immune response decreases the number of gonococci expressing the homologous Opa protein in vivo; iii.) expression of a gonococcal catalase-reporter gene fusion will be measured during murine infection and in neutrophil adherence assays to study the regulation of gonococcal catalase in response to inflammation. A transcriptional gene fusion bank using the green fluorescent reporter gene will be constructed and screened for promoters that are expressed during experimental murine infection; genes identified under these conditions will be cloned for further study.